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Old Jul 30, 2006, 11:09 PM
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Classic Runabout's Tight Prop Shaft...HALP!

I recently bought a Pro-Boat Classic Runabout and am in the process of tweaking, twiddling and repositioning things to make it into a standoff scale model that has good running characteristics. In the process of fitting a replacement flex-joint for the original dogbone U-joint I had to pull the prop shaft for greasing. After liberally applying lithium grease I put her back in place but I notice there's what I think is really unwanted resistance when I turn the prop/shaft by hand. Since the shaft tube is well and truly glued in place I'd not like to try and replace it. The prop shaft is pretty dang straight when I put a straight edge to it.

Any suggestions as to how to reduce all the drag on the system?

Tim Stolle
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Old Jul 30, 2006, 11:15 PM
Drydock Captian
Massey's Avatar
Spanaway, WA
Joined Jul 2006
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I take it that this is a solid shaft drive? The usual cause of bimding is the prop's lock nut being too tight against the stuffing tube. I make mine snug then put the prop on till it is finger tight against the nut then I use a small wrench or needlenosed pliers to tighten the nut against the prop. This does two things; First it locks the prop in place so it does not come off the shaft, and second it gives the shaft a little fore and aft play (if done right the play is less than 1 mm). You want a little play in the shaft for reduced friction and to help compensate for the forces that the prop will exert on the shaft and hull. Hope this helps

Massey
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Old Jul 30, 2006, 11:34 PM
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It is indeed a solid shaft drive...3 mm shaft running in a brass stuffing tube. I just checked the shaft for "end play". Actually there's too much end play right now...it needs some adjusting before I put the motor back in. The shaft can move in and out a few millimeters as it currently sits. The problem is, when I twist the shaft by hand I still feel what seems to be excessive drag in the system. I'm wondering if I couldn't take off the prop (plastic sucker) and run the shaft with an electric drill for a while to wear it in some and mebbe get rid of some of the drag. Got any other ideas I might try?

Tim
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Old Jul 31, 2006, 12:13 AM
KC8WPF
CG Bob's Avatar
Euclid, Ohio, United States
Joined Sep 2004
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Lots of good information on this boat at this thread. Most people seem to be replacing the stock dog-bone with a plastic u-joint; replace the stock prop with a metalone.
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Old Jul 31, 2006, 12:59 AM
Sea Dragon-Lover
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PDX, OR
Joined Dec 2002
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Was the shaft like this before you applied the grease?

It IS possible to put too much grease into a stuffing tube.
The binding will get worse if you put it into a cold lake or river also.
I've done this...

Try using the prop shaft to push some of the grease throught and out the inside end of the stuffing tube. at least a third of what you think you put in.
If that doesn't help free up the shaft, then check the bearing ends for binding.
I liked to have no more than a millimeter of play between the propeller and the stuffing tube.
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Old Jul 31, 2006, 01:18 AM
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Bob, I'd corresponded with Jim Duda right after I bought the boat and got all the scoobydoo on the mods he tested out. I replaced the stock dogbone with one of the recommended flex-couplers and that worked out just fine. I also bought an Octura metal prop...it still needs sharpening and balancing before installation. I bought the recommended motor and the ESC with reverse so I'm as set as I can be if I can get rid of the darn drag in the shaft/stuffing tube system. Since I know it's not due to any binding from being set up too tight with no available end play, the drag has to be caused by the prop shaft rubbing on the stuffing tube someplace. There can't be much of a kink in the system since the shaft slides into place with very little force needed.

Tim
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Old Jul 31, 2006, 01:25 AM
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Umi, the shaft was worse before I swapped out the dogbone U-joint. It "cogged" a whole lot becasue it was way too tight with no end play to speak of. It's much better than it was but I will try and get rid of some of the grease I put on the shaft. I can run a pipe cleaner down the stuffing tube and take out a bunch of it for certain and can easily pull out the shaft and wipe that off.

Just now it dawns on me that I can use a small reamer and just open up the tube and strut ends a little bit. Might be that there's some burring there.

Tim
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Old Jul 31, 2006, 01:26 AM
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Am I right in thinking that the prop shaft should turn very freely in the stuffing tube or is there some degree of drag inherant in that kind of system?

Tim
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Old Jul 31, 2006, 01:41 AM
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one thing that might help...is to use some steelwool to polish the shaft(or some baking soda on a damp rag). next if that didn't do the trick is a bit of 'brasso'(brass/chrome polish)one or two drops in the stuffing tube and spin the shaft at low speed for a minute. then clean a)the shaft and b) the tube(small cotton ball works nicely, then relube. hth
rex
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Old Jul 31, 2006, 04:22 AM
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McAlester
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Tim,
There will always be some 'drag' because of bearing surfaces, but, that drag shouldn't be much at all. Certainly not enough to be able to feel or hear any dragging (boy, is that 'subjective'!). 'Rex_R's suggestion is one to at least keep in mind. I'm not real sure it would be the first thing I tried, but it might be the second... Good luck!
- 'Doc
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Old Jul 31, 2006, 08:42 AM
Drydock Captian
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Spanaway, WA
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You have to remember also that while the grease is a lubricant it is also very thick and will cause drag. It should turn freely with resistance but not bind on anything. If you spin the prop with your fingers really hard it should not keep spinning, if it does then you dont have enough lube in the shaft. Like Umi said tho too much will cause excessive binding as well. Good luck

Massey
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Old Jul 31, 2006, 10:21 AM
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Central Missouri,USA Along the banks of the Missouri River
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Tim,

Ive got a runabout and have experienced someof the same problems.I found that the motor was at the wrong angle,thus causing too much drag.The motor shaft was alot lower than the end of the dogbone,so i took the motor off put some small washers under the rear two motor mounting screws.I think this helped as well as a new flex shaft.
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Old Jul 31, 2006, 10:59 AM
Ray Farina
Northeast Pennsylvania
Joined Jan 2006
244 Posts
If you have brass tubes check and make suse you do not have any shavings on the inside of the end of the tubes. Take a small swiss round file and make sure that the inside ends of your shaft are clean.
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Old Jul 31, 2006, 01:58 PM
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Eureka! I found the source of the prop shaft drag...at least the location of same. I took out the shaft and slowly reinserted it into the tube and the resistance occurs at the point where the stuffing tube enters the inside of the hull. I suspect it may be that the stuffing tube is just a tad bent...trouble is, is it bent up, down or sideways?

Tim
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Old Jul 31, 2006, 03:48 PM
Drydock Captian
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Spanaway, WA
Joined Jul 2006
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Clean out the grease and look into it and see if you can tell from the inside. Or as you insert the shaft watch or feel what way it changes direction at the point of the bend then you know it is the exact oppisite direction ( if the tube pushes the front shaft to the left then the back (part in your hand) will move to the right) so the tube will need to move a little in the direction of the end of the shaft. Is that confusing to you? I understand what I am saying but I am not sure I explained it totally clear. I can try again if you need.

Massey
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